Lenticular image, as used herein, describes the class of images that are formed on the back side of a lenticular support or substrate and which provide the ability to selectively view at a certain viewing angle a single image from a set of images. The lenticular substrate is a parallel array of cylindrical lenses, or lenticules, made of a suitable clear material which forms the substrate onto which specially formatted image data is applied. This specially formatted image data as described in the art, consists of separate, parallel image lines or image views placed behind and along the length of each lenticule. These image view lines are alternatively called lineform or integral image data. There are usually many distinct image view lines arranged in parallel behind each lenticule. As the number of view lines behind each lenticule increases, the spacing between each line must decrease proportionally for a given lenticule size. It is not unusual to have image view line spacing on the order of 12 to 15 microns or less depending on the imaging technology used to generate the images.
The thickness of the lenticular substrate is designed so that when the image data is applied to the back surface of the substrate, the image view lines will be located at the back focal distance of each of the individual lenticules. This allows each image view behind a given lenticule to be seen through the lenticule separately from the other image views as the lenticule is observed at different view angles. This is because the cone of light that emanates off a view line, either from transmittance or reflection, to the lenticule lens surface refracts and forms a mostly parallel ray of light exiting the lenslet at an angle determined by the placement of the view line relative to the lenticule. The width of the parallel rays emerging from the lenticule will have the same width as that of the lenticule and thus the view line's width will be seen magnified to that of the lenticule.
The resolution of a lenticular image, in the direction perpendicular to the lenticules, will always be equal to the pitch of the lenticular array. The actual number of different images that can be seen as the viewing angle changes will be the number of image lines placed behind each lenticule. Of course there will always be a practical limit on exactly how many distinct views can actually be resolved. This limit will be determined by such things as the optical quality of the lenses of the lenticular substrate, the resolution of the media used to form the image lines and the manufacturing tolerance for the thickness of lenticular substrate.
Viewing of individual images is accomplished by the cylindrical lenses and the fact that they restrict the view each eyes sees. The changing of views that are visible to each eye is accomplished by changing the viewing angle of the eyes relative to the centerline of the lenticules. This means that either the lenticular media must be rotated or the location of the viewers eye must be physically moved to see the different image views of the lenticular image. Therefore, small lenticular cards are usually held in the hand and rotated, while large lenticular images are usually backlit and firmly mounted with the lenticules in the vertical direction, requiring the viewer to walk past the lenticular image.
Depending on the content of the original source images and how these source images are formatted and applied to the lenticular array substrate, different lenticular image effects can be produced. If the original image source data contains multiple parallax images of a scene, the data can be formatted onto the lenticular substrate in such a way as to produce an autostereoscopic image. In this instance the lenticules are oriented vertically as a person views the stereo image. Since each eye views the lenticules from different angles, each eye sees different views behind the lenticules and the image appears to have the quality of depth.
Another common use for lenticular imaging is to view motion or dynamic image content. In this case a temporal image sequence, which might be from a video clip, is sampled, formatted and applied to the lenticular substrate. When used in this application the lenticules are oriented horizontally and in this case each eye will see exactly the same view. The lenticular image can then be rotated by hand along the horizontal axis of the image so that the eyes see sequences of image views producing the effect of motion or scene change.
Another variation is to place several different image scenes in sequence together on one lenticular card forming a collage. The images may be thematically related but the individual images themselves are usually different pictures. Thus the images may be scenes relating to a family vacation or perhaps a wedding. The number of individual pictures displayed on this type lenticular card is usually limited to two to four. This is due to the fact that as more pictures are added to the lenticular card each individual picture will be seen over a smaller total viewing angle. This makes it difficult for the person viewing the card to see only one image at a time.
It is desirable to have a lenticular image made up of photographs of an individual taken at different periods in an individuals life and that give the appearance of the individual aging as the image is rotated.